Process for coordinated cleaning and flow brightening of tinplated steel



Nov. 3, 1970 E. P. SPENCER HAL PROCESS FOR COORDINATED CLEANING AND FLOW BRIGHTENING 0F TINPLATED STEEL Filed Jan. 19, 1967 FIGI FIGZ mvmons EDWARD P SPENCER REX L. mums JON C. WILLIAMS #5 M TTORNEYS United States Patent 3,537,917 PROCESS FOR COORDINATED CLEANING AND FLOW BRIGHTENING OF TINPLATED STEEL Edward P. Spencer, Stenbenville, Ohio, Rex L. Landis,

Weirton, W. Va., and Jon C. Williams, Steubenville, Ohio, assignors to National Steel Corporation, a corporation of Delaware Filed Jan. 19, 1967, Ser. No. 610,428

Int. Cl. B44d 5/00; C21d 7/02, 9/52 U.S. Cl. 148-12.1 7 Claims ABSTRACT OF THE DISCLOSURE Method and apparatus for continuous strip processing of tinplated flat rolled steel, such as tinplated steel foil, which is simultaneously flow-brightened and cleaned of rolling lubricant by passing the product longitudinally through a heating zone in which the product is raised to a temperature suflicient to melt the tinplating and substantially simultaneously vaporize the rolling lubricant. The position of the melt line of the tin is defined by a cloud of evolving lubricant which is sensed by photocell detectors, or the like, to automatically control heating of the product to facilitate proper flow brightening. Coiling of light-gauge material is facilitated by blowers which maintain the product in the fiat, fold-free configuration.

Processes of manufacture of light gauge tinplated steel strip have been developed which involve the plating of steel strip with a layer of tin and then cold reducing the plated product. To successfully perform this cold reduction, it is necessary to lubricate the rolls and the strip being reduced. As a result, the cold reduced plated product is coated with rolling lubricant.

For many applications of this cold reduced plated product, it is necessary that the product have a clean surface. For example, in the manufacture of containers the surface of the product must be sufficiently clean to permit laminating, lacquer coating, or printing with decorative or informative matter.

Existing methods for removal of this rolling lubricant involve passing continuous strips of cold reduced product through a tank of solvent material. These methods do not provide adequate cleaning and are not satisfactory for very thin materials because of wiping and handling difiiculties.

The present invention includes solution of the above cleaning problems and a new product, flow-brightened tinplated steel foil. A separate problem associated with the processing of very thin tinplate, e.g., tinplated steel foil, is temperature control during flow brightening. With light gauge materials, slight variations in thicknesses of the steel substrate and tin coating require very close temperature control during a flow brightening process. Otherwise, excessive heating will result in formation of an unduly thick tin-iron alloy layer and excessive oxidation of the molten coating, to the detriment of the product. Insufficient heating will result in failure to flow brighten properly. Conventional temperature sensing means are neither fast enough nor sufliciently accurate to adequately control flow brightening of light gauge materials, such as tinplated steel foil.

Accordingly, a main object of the invention is the provision of improved processes and apparatus for cleaning and flow brightening light gauge tinplated steel which solves these problems of the prior art.

Stated more specifically, an object of the invention is the provision of processes and apparatus for coordinated cleaning and fiow brightening of tinplated steel.

Other objects and advantages of the invention will be evident from the following detailed description which,

ICC

when considered in connection with the accompanying drawings, discloses a specific embodiment of the invention for purposes of illustration only and not for definition of the invention. For determining the scope of the invention, reference can be made to the appended claims.

In the drawings, wherein similar reference characters denote similar elements throughout the various views:

FIG. 1 is a diagrammatic representation of a preferred embodiment of the invention; and

FIG. 2 is a detailed view, schematically showing sensing means utilized in the embodiment of FIG. 1.

Referring to FIG. 1, a continuous strip 10 of light gauge tinplated steel is passed from a coil 12 on payoff reel 14, over bridle rolls 16 and 18 into a heating furnace generally indicated at 20. Heating furnace 20 can include an entry portion generally indicated at 22, an intermediate portion generally indicated at 24, and an exit portion generally indicated at 26. Tension is maintained in strip 10 by takeup reel 28, onto which the strip 10 is recoiled after passing over bridle rolls 30 and 32 upon emerging from heating furnace 20.

Heating means 34 in heating furnace 20 are elongated and extend transversely across strip 10, above and below the strip, to effect rapid heating of the strip uniformly across its full width. Heating means 34- are spaced in the direction of strip travel through the heating zone. In the embodiment of FIG. 1, heating means 34 take the form of elongated infrared heaters, although it is contemplated that other suitable types of heating means, such as high frequency induction coils, may be used.

According to the invention, a residue-free rolling lubricant having a vaporization temperature which is not higher than the temperature at which the tinplating is to be flow brightened is selected for cold reduction of the strip after plating. The cold reduced strip, having a coating of such lubricant, is then rapidly heated in heating furnace 20 to a temperature between about 450 F. and about 550 F., preferably about 450 F., to melt the tinplating and substantially simultaneously vaporize the rolling lubricant, while avoiding formation of an excessive tin-iron alloy layer and excessive oxidation of the molten tinplating. Thus, the tinplating is flow brightened and the rolling lubricant is vaporized in a single treatment. That is to say, cleaning and flow brightening are coordinated. The flow brightened strip is rapidly cooled, as by passing between forced air blowers 36, disposed adjacent the exit portion of the heating zone. Watercooled chill rolls 30 and 32 supplement the cooling supplied by blowers 36 in addition to their guiding function. It should be observed that both heating and cooling are conducted rapidly to avoid excessive alloying and excessive oxidation of the tinplating.

In the preferred practice of the invention, the rolling lubricant selected has a vaporization temperature which is the same or substantially the same as the melting temperature of the tinplating. When the tinplating melts, the lubricant vaporizes as a narrow cloud 38 extending transversely across the strip 10. Vaporized lubricant evolves from the bottom surface of strip 10 (not shown) in a manner similar to cloud 38. The narrow cloud of vapor defines the edge of melting tinplating, since the lubricant vaporizes rapidly at the melt line of the tinplating. Flow brightening is identified by the oil vaporization and the heat of vaporization of the oil at the melt line takes heat from the molten tin and helps avoid substantial tiniron alloying.

Infrared heating means 34 may be individually controlled, and in any event are constructed and operated to heat the strip uniformly across its width to flow brightening temperature during passage of the strip through the intermediate portion 24 of heating furnace 20, so that vapor cloud 38 evolves from the strip at a location, generally indicated at 40, in the intermediate portion 24 of heating furnace 20. Once this condition is established, according to the preferred practice of the invention, accurate control over the cleaning and flow brightening is obtained by increasing and decreasing heating of the strip, by reference to the vapor cloud, since unavoidable minute variations in thickness of the steel substrate, the tin coating or the oil coating render it impossible to accurately control the process by setting the furnace at a fixed temperature.

A length of strip which has a thicker steel substrate, tin coating or oil coating, than other portions of the strip, would ordinarily be required to traverse a greater portion of the heating zone before it is heated to flow brightening temperature when operating at a fixed temperature. With the present invention the flow line and the vapor cloud which marks the flow line move toward the exit portion 26 of heating furnace 20. By sensing this movement and increasing heating of the strip so that less of the heating zone must be traversed before the strip is heated to flow brightening temperature, the flow line and the vapor cloud are moved back to location 40 in intermediate portion 24 of heating furnace 20, and the danger of material passing out of the heating zone without flow brightening is avoided.

Conversely, a length of strip which has a thinner substrate, tin or oil coating would traverse a shorter portion of the heating zone in a fixed temperature furnace before being heated to flow brightening temperature. This would create the danger of overheating the strip which has undergone premature flowing since a large portion of the heating zone must still be traversed while the tinplating is molten. Formation of an undesirably thick irontin alloy layer and excessive oxidation of molten coating may result. This is avoided, according to the invention, by decreasing heating of the strip when the vapor cloud moves toward the entry portion of the heating zone, thereby increasing the distance in the heating zone through which the strip must pass in order to be heated to temperature. This results in the movement of the vapor cloud back to location 40 in intermediate portion 24 of the heating furnace 20.

According to the invention heating of the strip may be altered by a number of techniques, for example, changing the speed of strip traveling through the heating zone and changing the heat output of the heating means 34. In effect the rate of heating of the strip is controlled. Although the first-mentioned technique assumes constant heat output from the heating means, and the second-mentioned technique assumes constant speed of the traveling strip, any combination of the two may be practiced to achieve the desired results. In practice, control of the heat output of infrared heaters or induction heaters is preferred since changes of speed can have undesired results when working with very light material.

Spaces are provided between heating means 34 to permit the passage of the vapor cloud upwardly and out of the system through fume catcher 42 and forced-air duct 44 which are associated with heating furnace 20. The strip may be passed horizontally through a heating zone, as illustrated, or vertically, in any event, the fumes from both surfaces of the strip are removed in a direction to avoid contact with the cleaned strip and thereby avoid contaminating the cleaned strip.

Lubricants having a vaporizing temperature not higher than about 550 F. may be used in the invention, although oils having a vaporizing temperature substantially equal to the melting temperature of the tinplating are preferred; mineral oil base lubricants are a specific example. Dependent upon subsequent processing operations, the lubricant selected should be vaporized to leave little or no residue.

For example, if the product is to be used in subsequent laminating operations it should be cleaned to classification A of the wettability test practiced in the foil industry. Basically, this is a test to determine whether water or a mixture of water and ethyl alcohol will wet a sheet of material. Sheets tested are classified as follows:

(A) deionized water;

(B) 10% ethyl alcohol, balance deionized water; (C) 20% ethyl alcohol, balance deionized water; (D) 30% ethyl alcohol, balance deionized water.

Product produced in accordance with the present invention has qualified readily for classification A of the above test.

In a preferred embodiment of the invention, means are provided for sensing movement of the vapor cloud away from location 40 in the intermediate portion 24 of the heating zone. An arrangement and operation of means for sensing movement of the vapor cloud are explained with reference to FIG. 2 of the drawings. In FIG. 2, strip 10 is shown passing longitudinally through the intermediate portion of the heating zone. Means are provided on one lateral side of the strip for passing beams of light transversely across the strip in the intermediate portion of the heating zone. In FIG. 2, these means take the form of light sources 46 and 48 which may be of any suitable type of conventional design, disposed on opposite sides of location 40 and connected by leads 47 and 49, respectively, to a suitable power source (not shown). On the remaining lateral side of the strip, photocell means 50 and 52 are provided, disposed to be responsive to the beams of light diagrammatically shown by dotted lines, which are passed transversely across the strip by light sources 46 and 48, respectively. Photocell means 50 and 52 are connected by suitable leads 51 and 53 respectively to controller 54 which may be of any suitable type of conventional design.

In one mode of operation according to the invention, controller 54 is operatively connected by leads 55 to the motor (not shown) which drives takeup reel 28 in FIG. 1, in a manner well known in the art to increase and de.- crease the speed of strip 10 by increasing and decreasing respectively the rate of rotation of takeup reel 28.

In this mode of operation, the speed of the strip is initially adjusted so that the vapor cloud defining the flow line evolves from strip 10 at location 40 in intermediate portion 24 of the heating zone. Thereafter, when the evolving vapor cloud moves toward exit portion 26 of the heating zone, the cloud intersects at least a portion of the beam of light passing from light source 46 to photocell means 50. The interruption of the light beam activates controller 54 to decrease the speed of the strip by slowing down takeup reel 28, thereby increasing heating of the strip so that the fiow line and vapor cloud which defines the flow line move back to location 40 in the intermediate portion of the heating zone. When the vapor cloud passes out of the beam of light passing to photocell 50, the controller is preferably operative to maintain the speed of strip travel as it is at that time until movement of the vapor cloud necessitates another adjustment.

Conversely, when the evolving vapor cloud moves to ward entry portion 22 of the heating zone, the cloud at least partially interrupts the light beam passing between light source 48 and photocell means 52. This activates controller 54 to increase the rate of rotation of takeup reel 28, thereby increasing the speed of travel of the strip and decreasing the rate of heating of the strip so that the flow line and vapor cloud returns to location 40 between the photocells. When the vapor cloud passes out of the beam of light passing to photocell 52, controller 54 operates to maintain the speed of the traveling strip as it is at that time until another change becomes necessary.

In another mode of operation according to the invention, controller 54, instead of increasing or decreasing the speed of strip travel through the heating zone, in-

creases or decreases heating of the strip by increasing or decreasing heat output from means 34. In this mode, the strip travels through the heating zone at a substantially constant speed, and leads 55 from controller 54 are operatively connected in a manner well known in the art to increase or decrease electrical current to heating means 34, thereby increasing or decreasing heat output of the heating means. Thus, when the evolving vapor cloud moves toward exit portion 26 of the heating zone and intersects the beam of light passing to photocell 50, controller 54 responds to increase the amount of electrical energy supplied to the heating means. When the vapor cloud passes out of the beam of light in returning to location 40 the controller is operative to maintain the heat output of the heating means as it is at that time until movement of the vapor cloud creates necessity for another adjustment.

Conversely, when the vapor cloud moves to intersect the beam of light passing to photocell 52, the controller is responsive to decrease current to the heating means. When the vapor cloud moves out of the beam of light, the controller maintains the heat output of the heating means as it is at that time until another adjustment is required.

It is to be understood that heating means 34 can include heating elements which may be selectively controlled. For example, heating elements at the entry side of the heating furnace 20 can establish a primary heating zone, and heating elements spaced further along the direction of strip travel can be used to established a control heating zone. A heating element, or elements, in the control heating zone can then be varied to obtain the precise control desired. Further it should be understood that selective control can be practiced automatically based on the teachings of the present invention by one skilled in the art.

It is contemplated that types of sensing means other than photocells, for example smoke detectors of conventional design such as are well known in the art, could be utilized to signal the movement of the vapor cloud to control means 54- It is also contemplated that photocell detector means can be used to sense the location of the flow line and con trol heating in response to movement of the flow line. In such a method cleaning is coordinated with flow brightening by detection of the flow brighten line on the product.

In the following examples of cleaning and flow brightening tinplated steel foil according to the invention, the foil had been rolled with a mineral oil type lubricant, each sample had a tin thickness of approximately x16- inches and each sample resulted in a class A cleanliness rating:

Processes and apparatus of the invention are particularly useful in cleaning and flow brightening tinplated steel foil which ranges in gauge from about 0.0001 inch to about 0.002 inch. The novel product of the present invention is produced by cold rolling matte-finish tinplate, of conventional gauges around .005 to .01, to foil gauge and cleaning and flow brightening in accordance with the process described. The inventive process and apparatus is also useful in treating .003 gauge and above. Tinplated flat rolled steel product as used in the claims is inclusive of foil and heavier gauge material.

The air blowers 36 serve an important function in addition to cooling the strip in that they maintain the tinplated steel foil flat for passage over cooling roll 30. Without this air blower function, the steel foil tends to fold over because of tension and form permanent creases, lengthwise of the foil, when passing over the cooling roll.

Special surface rolls, such as cork surface rolls, can prevent formation of creases when working with steel foil, but the cooling function of the rolls is lost. Specially shaped metallic rolls, or metallic rolls with surface patterns, such as a herringbone surface, will not keep steel foil flat because the steel foil does not stretch. Therefore the air blowers serve important strip confirmation functions in combination with a cooling roll.

The air blowers are ordinarily positioned shortly after exit of foil from the furnace and a cooling roll can be positioned downstream of the air blowers shortly after the foil passes the air blowers. With air blowers 36 only a single cooling roll is required and the foil can then be coiled directly after passage over the cooling roll.

Use of processes and apparatus according to the invention is highly advantageous. By cleaning light gauge tinplate according to the invention, the problems heretofore associated with wiping and handling of light gauge, highly flexible material in solvent baths is avoided. Moreover, by cleaning and flow brightening in a single operation, the time and expense involved in conducting separate operations is avoided. Furthermore, by coordinating cleaning with flow brightening, the control problems inherent in flow brightening, thin gauge tinplate heretofore encountered are avoided because a system providing close and accurate temperature control is provided by the invention. Still further, vaporizing lubricant cools the strip by extracting at least a portion of its latent heat of vaporization from the molten tin, and thereby assists in preventing excessive alloying during flow brightening. Also, it has been found that material treated according to the invention has a better, brighter, surface appearance and is more resistant to corrosion than that of the prior art. Finally, the system herein disclosed requires relatively little line space. Prior art cleaning systems, involving washing and scrubbing or electrostatic cleaning require a large amount of line space compared to that required by processes and apparatus according to the invention.

What is claimed is:

1. Continuous-strip process for coordinated cleaning and flow brightening of tinplated flat rolled steel product comprising cold rolling tinplated steel to form flat rolled steel product of desired gauge using a rolling lubricant selected to have a vaporization temperature coordinated with the melting temperature of the tinplating on the steel strip,

passing the flat rolled steel product coated with rolling lubricant longitudinally through a heating zone, heating the fiat rolled steel product in the heating zone to a temperature sufficient to melt the tin plating on the flat rolled steel product and substantially simultaneously vaporize the rolling lubricant, and then cooling the flat rolled steel product to solidify the molten tinplating.

2 The process of claim 1, wherein the rolling lubricant has a vaporization temperature which is not higher than about 550 F. and the flat rolled steel product is heated to a temperature between about 450 F. and about 550 F.

3. The process of claim 1, further including the step of pneumatically removing vaporized rolling lubricant at a substantial angle to the surface of the flat rolled product in a direction to avoid contamination of the cleaned fiat rolled steel product.

4. The process of claim 1 further including the step of contacting the heated flat rolled steel product after passage through the heating zone with gas under pressure to maintain desired configuration in the flat rolled steel product.

5. The process of claim 1, further including the step of detecting melting of the tinplating on the heated fiat rolled steel product by sensing vaporized rolling lubricant, and responsive thereto,

controlling heating of the flat rolled steel product to cause desired flow brightening and cleaning of the tinplating While avoiding formation of excessive tiniron alloy layer and excessive oxidation of the tinplating.

6. Continuous process for coordinated cleaning and flow brightening of tinplated steel foil comprising cold rolling tinplated steel strip to tinplated steel foil having a gauge between about .0001" and .002" using a rolling lubricant selected to have a vaporization temperature coordinated with the melting temperature of the tinplating on the steel strip,

passing the tinplated steel foil coated with rolling lubricant longitudinally through a heating zone,

heating the tinplated steel foil in the heating zone to a temperature suflicient to melt the tinplating on the foil and substantially simultaneously vaporize the rolling lubricant,

detecting melting of the tinplating on the steel foil, and

controlling heating of the tinplated steel foil responsively to detection of melting of the tinplating on the 7 i 8 steel foil to cause desired flow-brightening and cleaning of the tinplating While avoiding formation of an excessive tin-iron alloy layer and excessive oxidation of the tinplating.

7. The process of claim 6 further including the step of impinging gas under pressure against the tinplated steel foil after passage through the heating zone to maintain a fold-free configuration in the tinplated steel foil.

References Cited UNITED STATES PATENTS 1/1935 Nieman 148-4 1/1967 Mayhew 148-456 US. Cl. X.R 117-64; 148156 

